<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <title></title>
    <script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.1.0.js"></script>
    <script>
        $(document).ready(() => {
            $('div').hover(() => {
                console.log('hover');
                $('button').css('display', 'block');
            }, () => {
                console.log('leave');
                $('button').css('display', 'none');
            });
        });
    </script>
    <style>
        button {
            /*display: none;*/
        }

        div {
            width: 500px;
            height: 300px;
            color: #fff;
            border: 1px solid;
        }
    </style>
</head>

<body>

    <div>
        <button>按钮</button>
    </div>
</body>

</html>
